Background: Sleep quality may be directly related with vitamin D serum level. Some studies found that people with lower vitamin D serum level experienced a lower sleep quality. Consequently, this study aimed at determining the effect of vitamin D supplements on sleep point and quality in 20-50 year-old people with sleep disorders.Methods: This double-blind, clinical trial was performed in Golestan Hospital of Ahvaz Jundishapur Medical Sciences University from November 2015 to February 2016 on 89 people with sleep disorders based on Pittsburgh Sleep quality index (PSQI). Participants of the study were selected based on inclusion and exclusion criteria. Patients under study were divided into two groups of vitamin D supplement and placebo recipients by random allocation. At the end of the study, the data on 89 subjects (44 in intervention group and 45 people in placebo group) were examined. Participants in intervention group received four edible pearls, each 50000 IU vitamin D, one in a fortnight. To placebo group, a placebo capsule (edible paraffin) was given one in a fortnight. Before and after intervention, Petersburg’s sleep quality questionnaire, Depression Anxiety Stress Scale (DASS-21) questionnaire, international physical activity questionnaire, general information questionnaire, sun exposure, vitamin D serum level and three-day food record questionnaire were assessed and recorded for all participants. To analyze data, Student's t-test, Chi-square test, ANCOVA, Mann-Whitney U test and Wilcoxon statistical tests were used.

Results: Mean score of Pittsburgh sleep quality questionnaire before and after intervention was 9.45±2.44 and 6.75±2.97 respectively (P=0.001) in interventional group and 10.51±3.14 and 9.73±3.04 respectively (P=0.18) in controls. Based on the results of the present study, at the end of the study score of Pittsburgh sleep quality questionnaire reduced significantly in vitamin D recipients as compared with placebo recipients (P=0.001).Conclusion: This study shows that the use of vitamin D supplement reduced sleep score (PSQI) or improved sleep score, reduced sleep latency, increased sleep duration and increased subjective sleep quality after modifying confounding variables in adult people with sleep disorder.